1. Field of the Invention
The invention relates to systems for informing users at stops in bus networks about waiting times for buses.
2. The Prior Art
More particularly, of such systems, the invention relates to those comprising:
firstly transmitter facilities for generating electrical signals representative of the distance between each bus travelling along a line of the network and the "next" stop served by said bus, and for transmitting said signals in particular over an electromagnetic path; and PA1 secondly receiver members associated with at least one stop and organized to receive said signals, to select from said signals those that concern said stop directly or otherwise, to generate data relating to the waiting time for each "approaching" bus on the basis of the signals selected in this way, and to display said data. PA1 the topography of the route followed by each of the waited-for buses, where "topography" covers, for example, the presence of traffic lights (and possibly even the times of day they are switched on), the widths of the streets taken, etc.; or PA1 past experience (e.g. congestion due to an open air market on a particular day of the week), etc. PA1 if the length between beacons used for measuring the past real average speed is relatively short, then the result of the measurement is highly sensitive to fortuitous real circumstances that may have an abnormal effect locally on traffic (roadworks, unexpected behavior of a vehicle, and the like); PA1 if each length between beacons used for measuring the past real average speed is, on the contrary, relatively long, then the measurement will give a result in which the real traffic conditions that obtain on the downstream portion of said length are swamped, at least in part, which downstream conditions are naturally of relatively greater importance in estimating the "average speed" factor exactly. PA1 the number of past average speeds is equal to two, being V.sub.1 and V.sub.2, said speeds being calculated respectively for a relatively long time and for a relatively short time immediately prior to the given instant under consideration, and the past average speed used in the calculation is a weighted average speed equal to .alpha.V.sub.1 +.beta.V.sub.2, in which formula .alpha. and .beta. are two constants; PA1 the sum of the two constants .alpha.+.beta. is equal to 1; PA1 the periods corresponding to calculation of the two past average speeds V.sub.1 and V.sub.2 are respectively of the order of 10 minutes to 20 minutes for the first speed and of the order of 30 seconds to 5 minutes for the second speed; PA1 the calculation means are organized to give progressively increasing weight to the average speed V.sub.2 corresponding to the shorter time as the instantaneous real distance between the "approaching bus" and the stop under consideration becomes shorter; and PA1 one of the past real average speeds of the bus is the real average speed as detected and recorded for at least one other bus preceding the bus in question.
In known systems of that kind, proposals have already been made for the data as displayed to be in the form specifically of the waiting times for the buses approaching the stops in question.
Each waiting time is deduced from the detected distance between a bus and the stop, and by making use of the average speed of a bus on its line.
This "average speed" parameter is generally in the form of fixed data that is recorded permanently in the corresponding calculation devices.
The use of such a constant value parameter can give satisfaction, particularly when buses are progressing normally along the line that includes the stop concerned by the display, i.e. when traffic conditions on the line are average, with account being taken of the time required for stops at traffic lights, of traffic density at the instant under consideration, . . .
However, the above-defined average speed can take values that are very different.
Of the factors which can change that parameter, a distinction should be drawn between those that are predictable and those that are not.
Predictable factors include the time of day at which the display is taking place: it is well known that urban traffic density varies considerably with time of day, with a bus being able to travel without impediment when traffic density is low, e.g. late in the evening, and on the contrary with great difficulty during the "rush" hours.
Other predictable factors that may be mentioned include the next:
Corrections can therefore be included systematically to correct the average speed included in the receiver members of the information system in order to take account of the said predictable factors.
However, it is not possible in that way to take account of unpredictable factors for example such as a traffic jam building up due to a collision between two vehicles, a parked vehicle blocking a bus lane, and the like.
To remedy that drawback, proposals have already been proposed whereby the "average speed" factor used for each of the waited-for buses is a variable, which variable is based at least in part on the real past average speed of said bus as previously measured and recorded, which speed relates to a predetermined length of the route of said bus, as defined by two fixed beacons (document GB-A-2 178 210).
The above formula gives results that are closer to reality than those obtained when using a constant for the average speed of each bus.
However it suffers from the next drawbacks: